It’s going to take longer than 3 months for him to start to calm down.
One thing you can do to help him learn to calm himself down is this simple exercise. Find a relaxed place in the house and sit on the floor with him. Gently place one hand on his neck and another on his lower back. Gently rub his neck and back while lifting the skin on his neck. Keep your hands on his body. Tell him “Easy” in soothing tones. When he finally relaxes and stretches out on the floor say “Good Easy” in a soothing, but approving tone. Do this several times a day. Do Not use a treat reward with this.
After you’ve done this for awhile he’ll relax more quickly. This is your cue that he knows what “Easy” means and has started to learn to calm himself down. It helps to teach the ‘sit’ command next and then, whenever he is frightened tell him (in the same ‘easy’ tone) to “Sit Easy.” This worked wonders with my “pancake dog.” You could actually see her sit and then relax into a sitting-slump as I said “Easy”
